The isotopic composition of mercury (Hg) was determined in cinnabar ore, mine-waste calcine (retorted ore), and leachates obtained from water leaching experiments of calcine from two large Hg mining districts in the U.S. This study is the first to report significant mass-dependent Hg isotopic fractionation between cinnabar ore and resultant calcine. Data indicate that δ202Hg values relative to NIST 3133 of calcine (up to 1.52‰) in the Terlingua district, Texas, are as much as 3.24‰ heavier than cinnabar (−1.72‰) prior to retorting. In addition, δ202Hg values obtained from leachates of Terlingua district calcines are isotopically similar to, or as much as 1.17‰ heavier than associated calcines, most likely due to leaching of soluble, byproduct Hg compounds formed during ore retorting that are a minor component in the calcines. As a result of the large fractionation found between cinnabar and calcine, and because calcine is the dominant source of Hg contamination from the mines studied, δ202Hg values of calcine may be more environmentally important in these mined areas than the primary cinnabar ore. Measurement of the Hg isotopic composition of calcine is necessary when using Hg isotopes for tracing Hg sources from areas mined for Hg, especially mine water runoff.

Corn {Zea mays L.) residue is being considered as a feedstock for biofuels production. The impact of removing corn residue on soil productivity is not well understood. A corn-soybean [Glycine max (L.) Merr.] rotation was established in 2000 to determine the effect of removing corn residue at three rates (37, 55, and 98%) on soil organic carbon (SOC) in the 0-to 5-cm layer of soil after 8 yr. The effect of cover crops {slender wheatgrass [Agropyron caninum (L.) Beauv.] In corn and lentil {Lens culinaris Medik. variety Morton) in soybeans} on SOC was also measured. As the rate of residue removal increased, soil organic matter (SOM), wet aggregate stability (WAS), C/N, and microbial activity decreased significantly. Although the effect was not significant, there was a decrease in SOC as the rate of removal increased. At the high residue removal rate, SOM analyzed by quantitative ^^C NMR contained an abundance of aromatic C structures, suggesting that less humified pools of soil C are not being replenished. The humin fraction of the soil had a reduction in SOC under the medium and high rates of residue removal without a cover crop and is likely beginning to be depleted. Bradford-reactive soil protein and immunoreactive soil protein were higher in soils with cover crops, likely due to increased plant diversity and extending the growing season to allocate more C belowground. Overall, the data suggest that the soil properties indicative of soil quality are negatively impacted by removal of corn residue.

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Diisocyanates (dNCOs) are the most commonly reported cause of chemically induced occupational asthma, but the ultimate antigenic form is unknown. Reactions of the three most common monomeric dNCOs, hexamethylene dNCO (HDI), methylene diphenylisocyanate (MDI), and toluene dNCO (TDI), with cysteine methyl ester (CME) gave the corresponding bis-dithiocarbamates (HDI-CME, TDI-CME, and MDI-CME). The dissociation kinetics of these bis-thiocarbamates, in aqueous conditions, was followed spectrophotometrically under varying pH and temperature conditions. Reaction of the adducts with methylamine or human serum albumin (HSA) produced diurea, monourea, and diamine products, and this was consistent with the base-catalyzed elimination reaction (E1cB) pathway being the dominant, but not exclusive, dissociation mechanism. The hydrolysis of the adducts was first-order with respect to OH(-) concentration and overall second-order (HDI-CME, k = 3.36 x 10(2) M(-)(1) min(-)(1); TDI-CME, k = 2.49 x 10(4) M(-)(1) min(-)(1); and MDI-CME, k = 5.78 x 10(4) M(-)(1) min(-)(1) at pH 7.4) with deviation from second-order when the dNCO had an aromatic functional group. Arrhenius plots gave activation energies (HDI-CME, E(a) = 70.6 kJ/mol; TDI-CME, E(a) = 46.1 kJ/mol; and MDI-CME, E(a) = 44.5 kJ/mol) that were consistent with the following order of stability: HDI-CME > TDI-CME > MDI-CME. Therefore, the stability of different dNCO-derived thiocarbamates in aqueous environments can vary greatly. Thiocarbamate dissociation rates and type of products formed may potentially influence antigenicity and subsequent hypersensitivity/toxic reactions following dNCO exposures.